1. FIELD OF THE INVENTION
This invention pertains to a control system which can advance an outgoing train of output pulses with respect to an incoming train of input pulses in accordance with a predetermined relationship while keeping both trains at a common frequency. The invention herein finds particular application in control systems used in electrically operated knitting machines and the like.
2. DESCRIPTION OF THE PRIOR ART
In knitting machines, the mechanisms which select the knitting needles utilized are electrically operated, and require response times which are known in advance. Moreover, such machines can be operated over a range of speeds.
When a knitting machine is operated at a slow speed, it is sufficient to operate the needle selecting mechanisms in synchronism with each revolution or part of a revolution of the machine, since at slow speeds the response times of the mechanisms in question is not detrimental to proper operation. However, as the speed of the knitting machine is increased, it becomes necessary to energize such mechanisms in advance, in order to have needle selection take place at the desired point in the machine's operating cycle. As the machine is speeded up, this advancement must be progressively increased in order to produce an accurately knitted product.
Thus, it has already been proposed to utilize control systems which advance needle selection in accordance with machine operating speed. For example, Federal Republic of Germany Auslegeschrift No. 14 63 031 and Federal Republic of Germany Auslegeschrift No. 20 55 100 pertain to control systems which will operate in this fashion. In the first of these two references, a control system is disclosed in which the entire speed range of the machine is divided into three stages. In that stage which encompasses the lowest operating speeds of the machine, no needle selection advance takes place. In the next stage of machine speeds, selection advance is increased but is constant within the stage in question. In the highest stage of machine speeds, selection advance is once again increased, and held at a constant value. Thus, in this reference needle selection advance is increased in discrete steps which are comparatively large. In the second reference, needle selection advance increases continuously as machine speed increases.
In both of these prior-art control systems, an analog selection advance is used. With analog control systems, there is no exact correlation between needle selection and machine speed, so that errors in needle selection arise which increase in magnitude with time. Moreover, with such analog control systems, long-term operation and temperature variation can adversely affect machine accuracy and therefore degrade the fabric produced.
Therefore, it would be advantageous to provide a control system for knitting machines and the like which would operate in a digital fashion in order to ensure that needle selection advance would take place in an exactly calibrated fashion, and in order to ensure uniformity in operation over long periods of time.